Differential imaging coronagraph for the detection of faint companions

One of the major problems in trying to observe a faint companion from the ground comes from atmospheric turbulence. We present here a new camera capable of subtracting the effect of atmospheric turbulence on the PSF by taking simultaneous images of a star at three different wavelengths centered around the 1.6 micrometers methane absorption band typical of brown dwarfs and jovian planets. It is to be used at the adaptive optics compensated foci of the Megantic 1.6m, the CFHT 3.6m and the Gemini 8.2m telescopes. We present its design, which results from experiences at Megantic and CFHT with various techniques. Simulations predict there will be a 15 magnitude increase in sensitivity for detection of faint companions.